The present invention relates generally to data security for computer systems. More particularly, the invention relates to an encryption apparatus which is automatically invoked during the computer system power-on routine and which automatically intercepts and encrypts data being written to removable data storage media. A complementary decryption procedure is automatically invoked when data is read from the removable data storage medium. The encryption apparatus thus discourages the taking of data from the computer system by copying it onto a removable medium for use on a different computer system without decryption capabilities.
Computer data is often stored on nonvolatile read/write media such as magnetic disks, optical disks, magnetic tape, and the like. Many popular computer systems of today use both fixed data storage media, which cannot be readily removed from the system by the user, and removable media, which are intended to be removed from the system by the user. For example, many popular microcomputer and minicomputer systems have nonremovable fixed disk or hard disk drives and removable floppy diskette drives.
Data is frequently stored on nonvolatile read/write media as records or files, which provide a degree of organization to assist in locating and retrieving the stored data. The manner of storage as records or files can be unique to a particular make and model of computer system hardware, or it can be standardized to be compatible with other makes and models of computer system hardware. The latter allows one to transfer data from one computer system to another compatible computer system by simply writing the data onto a removable medium, such as a floppy diskette, removing the diskette to the other computer system and then reading the data from the diskette.
With the proliferation of affordable compatible computer systems, the ability to share data in this fashion represents a significant security problem to businesses which store and process confidential and proprietary information using computer systems having the capability to support removable media. For example, a business might store confidential or proprietary information on its computer system fixed disk or hard disk, where the information can simply copied onto a floppy diskette and removed from the premises.
A number of different security measures have been contemplated to combat this problem, although many such measures make it more difficult for users who use these systems on a daily basis. Also, incompatibilities with different types of application software products frequently arise when security systems are in place. This can render the computer system inoperative or unreliable.
Part of the compatibility problem can be attributed to the fact that there is presently less than adequate standardization in the manner in which application programs interface with the computer system's underlying operating system. The operating system provides an environment in which the application program runs. Application programs are thus written to interface with the operating system, with the desire that the workings of the operating system will be transparent to the user. However, many conventional security systems alter the manner in which application programs interface with the operating system environment. This can lead to compatibility problems. The risk of encountering compatibility problems with conventional security systems in place is considerable, particularly since it is often not feasible to test all available application programs which a user may wish to run under the operating system environment. As an example, a conventional security system may work properly for a particular spreadsheet program, but may intermittently and unexpectedly corrupt the data produced by a particular word processing or accounting program. This is clearly undesirable.
The present invention overcomes the limitations and compatibility problems of conventional security systems by providing a security system which automatically encrypts all data written to removable media, and which similarly decrypts all data read from that media. The invention works in a way which is completely transparent to the user and to the application program. The invention may be implemented without requiring use of passwords. This is a decided advantage, since password security is only as reliable as the persons having knowledge of the password. The invention is capable of being implemented on both stand alone and networked computer systems.
Rather than attaching to the computer system software at the disk operating system level as many conventional data security systems do, the invention attaches to the more primitive, computer hardware specific BIOS or Basic Input Output System level. Attaching to the computer system at the BIOS level, the invention must be implemented with a particular computer system hardware in mind. This has advantages over the conventional approach of attaching at the higher disk operating system or DOS level, where compatibility with a plethora of application programs must be kept in mind.
The invention provides a data security system for a computer system having a fixed data storage medium, a removable data storage medium and a buffer area for communicating with the fixed and removable data storage media. The security system comprises a security means communicating with the buffer area for automatically intercepting and encrypting data flowing from the buffer area to the removable data storage medium without intercepting and encrypting data flowing from the buffer area to the fixed data storage medium.
In a presently preferred environment, the computer system has a processor for operating on data comprising arrangements of binary digits. The computer system has a power-on routine for causing the processor to scan a predetermined range of memory location addresses for instructions after power-on. The system includes a means for enabling the processor to communicate with the data storage media comprising program means for reading and writing data to a fixed data storage medium and to a removable data storage medium. The data security system of the invention comprises a security program disposed within the predetermined range of memory location addresses scanned by the power-on routine. The security program attaches itself at the BIOS level during the power-on routine and automatically alters the program means for reading and writing data to the removable data storage medium. The security program is capable of transforming data communicated between at least one of the fixed and removable data storage media and the processor. The transformation is conducted so that data stored on the one data storage media is represented using a different arrangement of binary digits than is used when the data is operated upon by the processor. Because the data is stored in a different arrangement of binary digits, the data will be virtually unintelligible when operated upon by a processor in a computer system which does not have the invention's decryption capability.
Further, the security system of the invention may be used in a computer system having a file storage structure for storing data as individual files on different portions of a removable data storage medium. The structure may include a file allocation table containing information for correlating the individual files with selected different portions of the medium. The security system comprises a means for encrypting and storing the file allocation information on the removable data storage medium. The invention further comprises a means, nonremovably associated with the computer system, for decrypting and using the information to correlate individual files with the selected portions of the medium, thereby permitting location and retrieval of data stored as files on the medium by the computer system.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.